(a) Technical Field
Polarization filters for use in optical systems and in particular in liquid crystalline displays.
(b) State of the Art
In Japanese Patent Application No. 62-70407, a method of producing a uniaxially oriented optically transparent film is described. Firstly, the surface of a support plate is oriented. A mixture comprising at least two liquid crystalline monomers and a photo polymerization initiator is provided on said plate. The monomers have a functional, polymerizable group in the molecule. The monomers used correspond to the formula ##STR1## wherein R is a hydrogen atom or a methyl group and X is a group of the formula ##STR2## or of the formula ##STR3## wherein Z is --CN or --F.
The mixture may comprise a dichroic colorant, a UV absorber and a spacer such as glass grains. Subsequently, the monomers are polymerized in the liquid crystalline state by exposing them to radiation using UV light or visible light.
(c) Problems to be Solved
The oriented film described hereinabove under (b) has the disadvantage that the orientation is completely lost when the temperature is increased to a level above the transition temperature nematic-isotropic. Consequently, the film is not temperature resistant, not even when the film is heated for a short period, for example, during the production process.